1. Field of the Invention
The present invention generally relates to the field of electronic noise rejection, and more particularly, relates to methods and apparatus for minimizing the effects of electromagnetic interference on physiological measurements.
2. Description of the Prior Art
Electronic monitors are currently used to measure various physiological parameters (e.g., blood pressure, heart rate, EKG, temperature) of patients during surgical procedures in the operating room (OR) and during care in intensive care units (ICUs). However, other electronic equipment in use in the OR or ICU (e.g., electrocautery or electrosurgical devices) can generate electrical interference which corrupts the measured signals and invalidates the displayed numeric readings and waveforms. Present monitors incorporate various means for minimizing this interference in EKG and blood pressure waveforms, but systems used to measure temperature and cardiac output remain susceptible to this type of interference.
A known method for performing cardiac output (CO) measurements employs heat and pulmonary artery catheters and relies upon the continuous measurement of pulmonary artery temperature and heater power to accurately compute cardiac output. For example, such a method is described by Yelderman in U.S. Pat. No. 4,507,974 and McKown et al. in U.S. patent application Ser. No. 510,897, filed Apr. 18, 1990. The delicate CO measurements made by such instruments must be free of corruption by electrical interference if these instruments are to be used reliably in the clinical setting. Unfortunately, since the most common source of electrical interference (electrocautery devices) can be used for prolonged periods of time and in an unpredictable fashion in the OR or ICU, the clinician cannot obtain reliable measurements at critical times without asking the surgeon to stop his or her procedure to allow the measurements to stabilize. Since time is of the essence in these procedures, interference of this type must be compensated or eliminated if the aforementioned CO measurement devices are to provide accurate measurements. The present invention has been provided to reject such electrical interference.